Wake Up Device for Communications System

ABSTRACT

The present invention teaches a communications system comprising a first communications device for receiving data and a wake up signal. The first communications device comprises an active mode of operation and a sleep mode of operation for reducing power consumption. Further, the system comprises means for switching the first communications device to and from sleep mode in response to receiving the wake up signal. Further, the system comprises a second communications device for transmitting data to the first device during its active mode, while transmitting the wake up signal to the first device during its sleep mode.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 11/598,241,filed Nov. 9, 2006, by Robert R. Rotzoll, entitled “Wake Up Device for aCommunications System”, which is a continuation of U.S. patentapplication Ser. No. 10/869,508, filed Jun. 15, 2004, by Robert R.Rotzoll, entitled “Wake Up Device for a Communications System”, now U.S.Pat. No. 7,142,838, which is a continuation of U.S. patent applicationSer. No. 09/899,370, filed Jul. 2, 2001, by Robert R. Rotzoll, entitled“Wake Up Device for a Communications System”, now U.S. Pat. No.6,760,578, which is a continuation of U.S. patent application Ser. No.09/129,258, filed Aug. 4, 1998, now abandoned, which in turn is acontinuation of U.S. patent application Ser. No. 08/424,827, filed Apr.19, 1995, now U.S. Pat. No. 5,790,946, which is a continuation of U.S.patent application Ser. No. 08/092,147, filed Jul. 15, 1993, nowabandoned, all of which are incorporated herein by reference.

TECHNICAL FIELD

The technical field relates to a communication system. Moreparticularly, the invention pertains to a multi-mode communicationssystem.

BACKGROUND

Recently, there has been increased research and development with respectto Radio Frequency Identification (“RFID”) device tags. These RFID tagsessentially comprise small radio transceivers attached to a movableobject. By coupling an RFID tag to an object, it has been the intent ofdevelopers of creating a system for tracking the whereabouts andidentification of the object.

Several RFID systems have been developed. Generally, these designs havebeen relatively large in size—approximately cigarette package—and havebeen generally fabricated using hybrid circuit techniques. Besides theirbulky size, the systems require the RFID tag to constantly remainactivated.

Recently, there have been several breakthroughs in techniques in thedesign and manufacture of RFID tags. Examples of these include “RadioFrequency Identification Device (RFID) and Method of Manufacture,Including an Electrical Operating System and Method,” U.S. patentapplication Ser. No. 07/899,777, filed on Jun. 17, 1992, now abandoned;“Anti-Theft Method for Detecting The Unauthorized Opening of Containersand Baggage,” U.S. patent application Ser. No. 07/921,037, Jul. 24,1992, now abandoned; “Electrically Powered Postage Stamp or Mailing orShipping Label Operative with Radio Frequency (RF) Communications,” U.S.patent application Ser. No. 07/928,899, filed on Aug. 12, 1992; nowabandoned; and “Modulated Spread Spectrum in RF Identification SystemsMethod,” U.S. patent application Ser. No. 08/032,384, filed on Mar. 17,1993, now U.S. Pat. No. 5,539,775, all commonly assigned to MicronSemiconductor, Incorporated, and all incorporated herein by reference.

It has been thus a design criteria that these RFID tags be light weightand inexpensive. However, these systems previously have not addressedthe need of low power consumption. Presently, RFID tags must be activeto detect their location, as well as additional information. As such,there is a need to develop a RFID tag communications system having anactive mode for receiving/transmitting data and a sleep mode forreducing power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a high level architecture of the present invention.

FIG. 2 is a flow chart illustrating the method of the present invention.

FIG. 3 illustrates a first embodiment of the present invention.

FIG. 4 illustrates a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Referring to FIG. 1, a wake up device for a communications system isillustrated. As shown, the system comprises a first and secondcommunications devices; a transmitter 10 and a receiver 12. Transmitter10 is coupled to antenna 5 in order to properly transmit data and a wakeup signal to receiver 12. Receiver 12 comprises a wake up receiver 20and a master receiver 25, which are both coupled to antenna 15. Further,receiver 12 comprises a switch, which enables the substantial energysavings. It should be noted that the issue of energy saving with respectto transmitter 10 is not important as it is not coupled to an RFID tag,unlike is receiver 12 in the preferred embodiment.

To accomplish these energy savings, master receiver 25 comprises atleast two modes of operation. In the preferred embodiment, the firstmode is referred to as an active mode of operation and the second modereferred to as a sleep mode. Further, wake up receiver 20 requiressubstantially less power for its operation than master receiver 25.

In the active mode of operations, master receiver 25 functions as atraditional receiver, capable of receiving data transmitted bytransmitter 10. By contrast, in order to reduce power consumption duringperiods of inactivity, master receiver 25 comprises a sleep mode. Duringsleep mode, master receiver 25 utilizes a minimal amount of energy forbiasing purposes. Thus, by utilizing this design scheme, a substantialpower savings from receiver 12 can be achieved, which directlycorresponds to the life expectancy of battery powered receiver 12. Forexample, in one receiver design, a 98% power savings has been observed.

Coupled between master receiver 25 and wake up receiver 20, is switch30. Switch 30 switches master receiver 25 between its mode ofoperation—i.e., active to sleep mode, as well as sleep mode to activemode—in response to the arrival of a wake up signal. As such,transmitter 10 transmits a wake up signal to receiver 12, which isultimately received by wake up receiver 20. Upon detecting the wake upsignal, a mode change signal is generated to switch 30. Accordingly,switch 30 changes the mode of operation of master receiver.

In the preferred embodiment of the present invention, switch 30 onlyswitches master receiver 25 from sleep mode to active mode. Here, uponreceiving wake up signal, wake up receiver 20 generates a mode changesignal to switch 30. In response, switch 30 senses the mode of operationof master receiver 25. Thus, switch 30 switches master receiver toactive mode upon sensing master receiver 25 as being in sleep mode.Contrarily, switch 30 is inactive upon sensing master receiver 25 asbeing in an active mode of operation. In this embodiment, masterreceiver 25 further comprises a timing scheme which switches masterreceiver from active mode to sleep mode. This timing scheme is enabledwhen a predetermined period passes in master receiver 25 withoutreceiving any data from transmitter 10. The length of the period isdependent on several design criteria including the system's applicationand environment, as well as the desired probabilities of error. In afurther embodiment of the present invention, switch 30, low powerreceiver 20 and master receiver 25 are all positioned on a radiofrequency identification (“RFID”) tag.

Referring to FIG. 2, a flow chart illustrating the method for reducingthe consumption of energy in operating a communications system of thepresent invention employing the architecture described herein.Initially, a wake up signal is transmitted by transmitter 10, andsubsequently, the wake up signal is detected by wake up receiver 20.Finally, the mode of operation of the master receiver 25 is changed inresponse to the detection of the wake up signal.

In one embodiment of the present invention, the step of detecting thewake up signal, itself, comprises a series of steps. First, apredetermined frequency is detected from the wake up signal. In theevent that that frequency is found, a predetermined data rate isdetected from the wake up signal. If that frequency is not found, masterreceiver 25 is kept asleep. In the event that data rate of transmissionof a certain number of bits per second is found, an output signal isgenerated. If that data rate of transmission is not found, masterreceiver 25 is kept asleep. This step of generating an output signalfurther comprises the step of comparing the output signal with areference voltage. By doing so, switch 30 is enabled upon detecting apredetermined frequency and a predetermined data rate of transmissionand master receiver 25 is woken.

Referring to FIG. 3, a first embodiment of the present invention isdepicted. In order to receive a wake up signal, an antenna 50 is coupledwith a frequency detector, realized by a first bandpass filter 55 havinga bandwidth and a radio frequency (“RF”) output. First bandpass filter55, operating in tandem with antenna 59, detects the frequency of thewake up signal. To avert the detection of noise as a wake up signal, thebandwidth of first bandpass filter 55 is substantially narrow.Nonetheless, in the preferred embodiment, first bandpass filter 55 mustdetect a predetermined frequency and a related harmonic.

While the present invention utilizes a narrow bandpass scheme forfrequency detection, it should be obvious to one of ordinary skill inthe art that the frequency detector can be realized using alternatehardware. For example, in place of a narrow bandpass filter, ageneralized filter having an output coupled directly with a comparatorwould achieve the identical functional purpose were the comparator alsofed a frequency reference or source. Another example would be aresonator circuit.

Coupled to bandpass filter 55 is an envelope detector 60. Upon receivingthe RF bandpass output from filter 55, envelope detector 60 demodulatesthe RF bandpass output into a first Base Band (“BB”) signal. Envelopedetector 60 achieves this objective in two steps. However, it should beobvious to one of ordinary skill in the art that the functionalobjective of envelope detector 60 can be realized by alternate means.Initially, envelope detector 60 rectifies the RF bandpass output bymeans of a rectifier. Subsequently, a low pass filter is employed forfiltering the rectified RF bandpass output and forming the first BBsignal.

Once the frequency of the wake up signal has been detected, the presentinvention employs a data rate detector for detecting the rate of datatransmission of the incoming signal, which thereby rejects out of datarate signals. As such, this design employs two means for assessing twocharacteristics of the incoming signal. Thus, by this approach, noiseand/or other sources will not falsely trigger the master receiver intowaking up.

The data rate detector can be realized by a second bandpass filter 70having a second bandwidth and a second BB signal as its output. To avertthe detection of noise as a wake up signal, the second bandwidth ofbandpass filter 55 is substantially narrow bandwidth. In one embodimentof the present invention, the second bandwidth is substantially narrowerthan the first bandwidth of the first bandpass filter. However, in thepreferred embodiment, the second bandwidth need only detect a singularfrequency without any harmonics.

While the present invention utilizes the herein described means for datarate detection, it should be obvious to one of ordinary skill in the artthat the data rate detector can be realized using alternate hardware.For example, a comparator scheme or resonator circuit could be employed.Further, digital circuitry could also be used to accomplish the samepurpose as the data detector described herein.

Further, coupled with second bandpass filter 70 is a second envelopedetector 75. In order to detect the data rate of incoming signal andascertain whether it is the wake up signal, second envelope detector 75generates an output signal corresponding to BB signal input receivedfrom second bandpass filter 70 by demodulating the BB signal input.Second envelope detector 75 achieves this objective in two steps.However, it should be obvious to one of ordinary skill in the art thatthe functional objective of second envelope detector 75 can be realizedby alternate means. Initially, envelope detector 75 rectifies the BBinput signal second bandpass filter 70 by means of a rectifier.Subsequently, a low pass filter is employed for filtering the rectifiedBB signal input. As a result of this architecture, second envelopedetector 75 generates an upward ramped step or a downward ramped stepoutput signal.

Coupled to second envelope detector 75 is a comparator 80. Comparator 80is employed to compare the output signal of second envelope detector 75with a voltage reference. By this arrangement, comparator 80 triggers aninternal wake up.sub. 1 signal. Wake up.sub. 1 signal is subsequentlyfed into control logic 85, which is coupled with a data processor 90,for waking up the master receiver 25.

In an alternate embodiment of the present invention, a second data ratedetector is utilized. Second data rate detector, being coupled to thefrequency detector, receives the first BB signal generated by the firstenvelope detector 60. The second data rate detector can be designed inan identical fashion as the first data detector described herein.

By this arrangement, comparator 80′ triggers an internal wake up.sub.2signal which is input into control logic 85, which is coupled with adata processor 90, for waking up the master receiver 25. By employingtwo data rate detectors, the wake up receiver can switch the data rateto be detected from the wake up signal. Here, switching logic 85 incombination with data processor 90 recognize the data rate to bedetected from the wake up signal. Subsequently, when a change isnecessary, a second data rate is selected as being the data rate to bedetected from the wake up signal for the purposes of waking masterreceiver 25.

Moreover, this two data rate detector scheme can also be employed forthe purpose of enabling the wake up receiver to switch modes ofoperation—i.e., sleep mode and active mode—as described hereinabove.Thus, when a first data rate is received, master receiver 25 is to bewoken in to active mode, while master receiver 25 is to be put intosleep mode when a second data rate is received.

In a further alternate embodiment of the present invention, a mixer 65is employed. Mixer 65 is coupled between first envelope detector 60 andsecond bandpass filter 70. Mixer 65 is used to provide a means forfrequency translating the RF bandpass output. The extent of thetranslation performed by mixer 65 corresponds to the local oscillator.The local oscillator, having a clock rate of f.sub.1 provides areference oscillating signal to the mixer 65.

Referring to FIG. 4, an alternate embodiment of the present invention isillustrated. The architecture disclosed here is further development ofan alternate embodiment of FIG. 3. Here, three data rate detectors areemployed. Third data rate detector, being coupled to the frequencydetector, receives the first BB signal generated by a first envelopedetector 1 10. The third data rate detector can be designed in anidentical fashion as the first and second data detectors describedherein.

By this arrangement, comparator 130″ triggers an internal wake up.sub.xsignal which is input into control logic 135, which is coupled with adata processor 140, for waking up the master receiver 25. By employingthree data rate detectors, the wake up receiver can switch the data rateto be detected from the wake up signal. Here, switching logic 135 incombination with data processor 140 recognize the data rate to bedetected from the wake up signal. Subsequently, when a change isnecessary, a third data rate is selected as being the data rate to bedetected from the wake up signal for the purposes of waking masterreceiver 25.

In still another embodiment of the present invention, a modulationdetector (not shown) is further incorporated for detecting a modulationscheme. In this embodiment, the wake up signal must also comprise amodulation format or formats. As such, the modulation detector candetect a modulation scheme selected from the group including at leastamplitude modulation, frequency modulation, amplitude shift keymodulation, phase shift key modulation, frequency shift key modulation,and multiphase frequency shift key modulation. The modulation detectorcan be realized by a variety of designs known to one of ordinary skillin the art. Thus, upon receiving the wake up signal, the modulationdetector detects the format of the wake up signal and respondsaccordingly.

All of the U.S. patents cited herein are hereby incorporated byreference as if set forth in their entirety.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

1. A method of tracking inventory, the method comprising: positioning aninterrogator unit in a first region, the interrogator unit comprisingone or more transceivers communicatively coupled to one or moreantennas, the interrogator unit being configured to transmit radiofrequency (RF) signals; transmitting by the interrogator unit via atleast one of the one or more transceivers a first RF signal; receivingby a first RFID tag the first RF signal; transitioning to a first modeby the first RFID tag when the first RFID tag determines the first RFsignal is at a first frequency and a first data rate; and transitioningto a second mode by the first RFID tag when the first RFID tagdetermines the first RF signal is at a second frequency and a seconddata rate, the first RFID tag remaining in the first mode untiltransitioning into the second mode upon receipt of the first RF signalat the second frequency and the second data rate, and the first RFID tagremaining in the second mode until transitioning into the first modeupon receipt of the first RF signal at the first frequency and the firstdata rate.
 2. The method of claim 1, wherein the first frequency issubstantially equivalent to the second frequency.
 3. The method of claim1, wherein the first RFID tag determines a frequency and a data rate ofthe first RF signal via one or more bandpass filters and one or moreenvelope detectors.
 4. The method of claim 1, wherein the first RFID tagconsumes less power in the first mode than the second mode.
 5. Themethod of claim 1, wherein the first mode comprises operating states inwhich the first RFID tag requires more power than operating states ofthe second mode.